FALLS LAKE PROJECT NEUSE RIVER BASIN, NC PERTINENT DATA Location of dam At Latitude 35 56', Longitude 78 34'; in Wake County, NC, about 10 miles north of Raleigh, North Carolina; about 198 river miles above New Bern, NC, and 235 miles above mouth; 47 miles upstream from Smithfield, North Carolina. Purpose For flood control, water supply, recreation, fish and wildlife enhancement, and augmentation of low flows for purposes of pollution abatement and water-quality control in the Neuse River Basin. Drainage areas (square miles) Eno River near Durham, NC -------------------------------- 141 Little River near Orange Factory, NC --------------------- 80 Flat River at Bahama, NC --------------------------------- 149 Neuse River at Falls Dam, NC ----------------------------- 770 Neuse River near Neuse, NC ------------------------------- 790 Neuse River near Clayton, NC ----------------------------- 1,150 Neuse River at Smithfield, NC ---------------------------- 1,206 Neuse River near Goldsboro, NC --------------------------- 2,399 Neuse River at Kinston, NC ------------------------------- 2,692 Reservoir Data Storage volumes: Inches Acre-feet Spillway design flood (elevation 289.2) ------- - 1,101,590 Standard project flood (elevation 271.3) ------ - 509,350 Top of flood control pool (elevation 264.8) --- - 352,577 Top of conservation pool (elevation 251.5) --- - 131,395 Bottom of conservation pool (elevation 236.5) - - 25,073 Bottom of sedimentation pool (elevation 200.0)- - 0 Uncontrolled flood storage (264.8-289.2) ------ 18.24 749,010 Controlled flood storage (251.5-264.8)--------- 5.39 221,182 Conservation storage (236.5-251.5) ------------ 2.59 106,322 Sedimentation storage (200.0-236.5)------------ 0.61 25,073 Sedimentation ------------------------------- 0.61 25,073 Water Supply -------------------------------- 1.10 45,000 Water Quality ------------------------------- 1.49 61,322 Surface areas (acres) Spillway design flood (elevation 289.2) ---- 39,960 Standard project flood (elevation 271.3) --- 26,440 Top of flood control pool, elevation 264.8 - 21,427 Top of conservation pool, elevation 251.5 -- 12,410 Bottom of conservation pool, elev 236.5 ---- 2,600 Bottom of sedimentation pool, elev 200.0 --- 0 Reservoir Coverage Counties affected ------------------ Wake, Durham, Granville Length at elevation 250 (miles): Along Neuse River -------------------------- 24 Along Eno River ---------------------------- 4 Along Flat River --------------------------- 3 Length of shoreline at elev. 250 (miles) --- 175 Reservoir Elevations (feet, m.s.l.) Top of Dam ------------------------------------ 291.5 Spillway design flood ------------------------- 289.2 Standard project flood ------------------------ 271.3 Flood of record (September 1945) -------------- 263.1 (Estimated) Flood of record (October 1999-Hurricane Floyd)- 264.34 (Actual) Top of flood control pool (spillway crest) ---- 264.8 Top of conservation pool (bottom flood pool) -- 251.5 Bottom conservation pool ---------------------- 236.5 Upper clearing limit (except for fish drops) -- 251.1 Elevation of guide acquisition line ----------- 264 feet mean sea level, plus 300 feet horizontally or 5 feet vertically (elev. 269 ft. m.s.l.), whichever encompasses the most area. Dam and Spillway Type -- Earth and rockfill (zoned), with side channel uncontrolled spillway, multilevel intake structure, and oblong-shaped conduit. Length of dam (feet) ---------------------------- 1,915 Length of spillway crest (feet) ----------------- 1,650 Spillway capacity at elevation 289.2 (c.f.s.) --- 39,500 Height of dam (feet) ---------------------------- 92.5 Freeboard (feet) -------------------------------- 4.3 Elevations (feet mean sea level) Dam: Top ----------------------------------------- 291.5 Base ---------------------------------------- 200.0 Spillway crest ------------------------------ 264.0 Outlet works Intake tower: Conduit intakes: Number -------------------------------------- 2 Size ---------------------------------------- 8.5 feet wide by 19 feet high each Invert elevation (ft., m.s.l.) -------------- 200 Exit invert elevation (ft. m.s.l.) ---------- 198 Piggyback gates: Number --------------------------------------- 2 Size ----------------------------------------- 12-inch square each (one per service gate) Invert elevation (ft. m.s.l.) ---------------- 208.75 Multilevel intakes: Number --------------------------------------- 4 Type ----------------------------------------- Drop inlet Size: Front -------------------------------------- Two, 8 feet square, invert elev. 231 ft., m.s.l. Left side (north) -------------------------- One, 8 feet square, invert elev. 241 ft., m.s.l. Right side (south) ------------------------- One, 8 feet square, invert elev. 241 ft., m.s.l. Conduit: Conduit length (feet) ---------------------- 272.5 Conduit equivalent diameter (feet) --------- 17.4 Maximum discharge at elev. 250 (c.f.s.)----- 10,000 (approximate) Stilling basin Minimum width (feet) ------------------------- 15.0 Maximum width (feet) ------------------------- 55.0 Length (feet-inches) ------------------------- 222-7 Bottom elevation (ft., m.s.l.) -------------- 185.4 End sill elevation (ft., m.s.l.) ------------- 188.4 Tailwater: Spillway design flood ---------------------- 221.6 Standard project flood --------------------- 210.0 Flood or record (September 1945) ----------- 204.5 Minimum (60 c.f.s.) ------------------------ 197.2 Estimated streamflows at dam (cubic feet per second) Preimpoundment (before normal operation began or before 7 Dec 1983: Mean discharge for period of record (60 years) -- 765 Minimum discharge: Instantaneous (30 September 1932) ------------- 5 Daily (30 September 1932) --------------------- 5 Monthly (September 1932) ---------------------- 18 Maximum discharge: Highest known (18 September 1945) ------------- 20,700* *(23,300 c.f.s. published by U.S. Geological Survey) Monthly (September 1945) ---------------------- 4,257 Bankfull discharge (approximate for downstream reach) ---------- 5,000-8,000 Postimpoundment (normal operation or after 7 December 1983): Maximum discharge: since filling of dam on 7 December 1983 Highest known (15 Sept. 1996--Hurricane Fran)-- 7,462 Peak Inflow to Falls Dam (6 Sept. 1996--Fran)---- 101,000 Standard project flood (cubic feet per second) Maximum estimated outflow ----------------------- 16,800 Maximum estimated inflow ------------------------ 153,500 Spillway design flood Derivation: Rainfall area-depth-duration derived by the Hydrometeorological Section of the Weather Service. Total average rainfall (inches) --------------- 23.80 Initial loss (inches) ------------------------- 0.70 Average infiltration rate (inches per hour) --- 0.04 Total storm runoff (inches) ------------------- 21.18 Peak inflow to full reservoir (c.f.s.) -------- 322,700 Regulated peak outflow (c.f.s.) --------------- 48,400